Chemical inhomogeneity of amphiboles in relation to section orientation in routine EPMA analyses

Abstract

Routine EPMA analyses of homogeneous amphiboles in amphibolites indicate significant compositional variation between sections with two cleavages and those with a single cleavage parallel to the c axis. Sections with two cleavages are enriched in SiO₂, MgO, MnO and CaO relative to sections with a single cleavage which are enriched in Al₂O₃, FeO_(total), TiO₂, Na₂O, and K₂O (i.e. ∑ of tschermakiteedenite substitutions). The degree of compositional variation between the different amphibole sections may, in part, be related to the extent of equilibrium attained in the rocks during recrystallization.